Grey Water Plumbing Layout Questions

[bjen5en]

I'm doing a shell-off renovation and have added all new tanks (2 grey @ 33 gallons each and 1 fresh water tank @ 50 gallons). I am going the composting toilet route so no black tank. The picture below is what I have designed for plumbing the 2 grey tanks together so far (this is all just dry fit at this point and tanks are just sitting on the frame) 1 tank will receive kitchen sink water and the other will receive bathroom sink water. I am planning on the shower drain to enter at the 90 deg elbow shown in the sketch (shower is at center bath on curb side). Both tanks will be vented and are below the floor. I figure this set up will allow water in the 2 tanks to "balance out" or "equalize".

Does this set up work?

Is there anything you would recommend changing?

Is it true that the shower drain will fill up the tank in this set up so long as the shower drain is above the tank?

[55AS]

Originally Posted by bjen5en

I'm doing a shell-off renovation and have added all new tanks (2 grey @ 33 gallons each and 1 fresh water tank @ 50 gallons). I am going the composting toilet route so no black tank. The picture below is what I have designed for plumbing the 2 grey tanks together so far (this is all just dry fit at this point and tanks are just sitting on the frame) 1 tank will receive kitchen sink water and the other will receive bathroom sink water. I am planning on the shower drain to enter at the 90 deg elbow shown in the sketch (shower is at center bath on curb side). Both tanks will be vented and are below the floor. I figure this set up will allow water in the 2 tanks to "balance out" or "equalize".

Does this set up work?

Is there anything you would recommend changing?

Is it true that the shower drain will fill up the tank in this set up so long as the shower drain is above the tank?

Water level should equalize as long as vents are working. Make sure you stay level.

[GeocamperAS]

The only concern with the shower draining into the piping rather than the side of the tank is when you dump the water from the tank rushing through the pipe, going past the wye of the shower, might cause a siphon effect and pull the water out of the shower trap. If that happens just add water to the shower trap after every time you dump.

[cliffcharb]

I would think you'd have a slow draining shower once the tanks start to fill up.

[GeocamperAS]

Originally Posted by cliffcharb

I would think you'd have a slow draining shower once the tanks start to fill up.

Good point. I would tend to agree

[HiHoAgRV]

It works fine, I've done that on a couple of instances. It's critical that the line have a vent between the pee trap and the tank.

[55AS]

Originally Posted by HiHoAgRV

It works fine, I've done that on a couple of instances. It's critical that the line have a vent between the pee trap and the tank.

Based on his layout I think it will be difficult to do that...

[tbashin]

If the shwr.has a vent between the p-trap and that low heel 90 it won’t siphon your p-trap when you drain the tank but you would be surprised how fast soap scum, hair , etc. can build up in a line. It will stay in the line as well as other residue from the tank can migrate into it because you are tying in at the low point. I would dump the shower into the tank so that residue hits open water sooner meaning less buildup in the line. I’m a plumber btw.

[bjen5en]

Originally Posted by tbashin

If the shwr.has a vent between the p-trap and that low heel 90 it won’t siphon your p-trap when you drain the tank but you would be surprised how fast soap scum, hair , etc. can build up in a line. It will stay in the line as well as other residue from the tank can migrate into it because you are tying in at the low point. I would dump the shower into the tank so that residue hits open water sooner meaning less buildup in the line. I’m a plumber btw.

Thanks everyone for all the info and feedback. Sounds like I would be better off going into the side of the tank which I can easily do. I can route shower drain into the side of the tank rather quickly after the P trap closer to curb side of the tank. If I do this do I still need to vent the line between P trap and tank? I'm not sure how I would accomplish this.

Also, are there any advantages to use a hepvO valve in lieu of a P-trap in this layout?

[HiHoAgRV]

Originally Posted by BambiTex

Based on his layout I think it will be difficult to do that...

An upward facing sweep T is what I've done. Just something to keep it from air locking when the tank level comes up above the bottom tube.

[Glenritas]

Defiantly use a hepv-O trap ! Or you may find the shower drain acting like a filler when the tanks are near full and driving to the dump station or down the road.

Casita uses a p trap and a shut off valve to prevent the shower filling from the tank when moving. The draw back is forgetting to open the valve before you get in the shower.

Cleaver Casitains have replaced the p trap and valve with a Hepv-O to solve both problems with great success.

[bjen5en]

Originally Posted by HiHoAgRV

An upward facing sweep T is what I've done. Just something to keep it from air locking when the tank level comes up above the bottom tube.

Not sure I follow. Are you saying to vent the line with an upward facing sweep t? Would an AAV work to vent this drain? It would have to be in the belly pan. Does that work? If not, I'm not sure how to vent this drain. Any suggestions or tips would be greatly appreciated.

Here's a couple rough sketches of what the plumbing will look like.

[HiHoAgRV]

Good drawings! I wasn't tracking that you were using hepvo valves. I haven't used AAV's with them because they are auto sealing. A pee trap will get sucked dry without an AAV and then let fumes back fill the room. Hepvo' don't have that issue. Instead of the AAV, tie that to the vent line. Why? If you fill the tank 1/2 way from the kitchen then you could trap air in the shower line. The water in the tank puts pressure on the air in that line and it forces the hepvo to stay closed until even more pressure is built up on the shower drain side (water backing up in the tub). Once the valve opens you get a big burp of the trapped air swapping sides with the shower water. The air has to come up into the shower.
If you replace your AAV with a vent, all of those issues go away.

My kitchen sink in the '63 is like this and I just haven't taken time to add the vent. Humm. I guess I do learn from my mistakes, I just don't do anything about it!

[tbashin]

Don’t put an AAV below the waterline. They aren’t designed to hold water pressure from what would be backflow when the tanks get full. You don’t want a leak in your belly pan. A vent through the roof is your best bet. Gray water coming up into the shower drain is your back up water level indicator showing its time to dump too. Can you tie a shower vent to the lavatory vent? It really doesn’t need to be a full size line to vent properly. 1” even would work...assuming you aren’t determined to meet any plumbing codes.

[dbj216]

I just don't see how your shower drain into the side of the holding tank is going to work except when the tank is nearly empty. The tank is big and has atmospheric pressure on the water surface as well as the weight of the water in the tank. The shower drain is small and has little "head" pressure. Tank water will back up into the shower drain pipe.

I envision trying to fill a fish aquarium with a hose at the bottom of the tank and pouring water into the hose. Not pumping it, just pouring it. The hose would fill up, wouldn't it.

Anyways, you can elevate your shower pan 3" so you can drain into the top of the tank? I know that works.

David

[bjen5en]

So what's the consensus? If I install a hepvO and route drain to enter tank on the side near the bottom, and I am able to vent the drain, will I have any issues with the shower draining and filling up the tank? I would really like to avoid going into the top of the tank because that means I have to build up the shower pan and lose precious head room height.
Thanks everyone for the feedback thus far.

[dbj216]

Run a little experiment. Maybe you folks have a flower watering can with a spout that comes out close to the bottom of the can.

If so, fill it the watering can half full of water. Then take a measuring cup or some other container and see if you can pour water down the spout and watch the watering can fill doing this. Or, will the water you try to pour down the spout just back up and drip on your shoes.

I believe you can fill a flower watering can from the bottom if you have a 6' long spout where you can create some "head pressure" in the water column and thus force the water into the bottom of the can.

I just don't understand how to fill a tank from the bottom without a pump. But I ain't a plumber either.

David

[bjen5en]

Originally Posted by HiHoAgRV

Good drawings! I wasn't tracking that you were using hepvo valves. I haven't used AAV's with them because they are auto sealing. A pee trap will get sucked dry without an AAV and then let fumes back fill the room. Hepvo' don't have that issue. Instead of the AAV, tie that to the vent line. Why? If you fill the tank 1/2 way from the kitchen then you could trap air in the shower line. The water in the tank puts pressure on the air in that line and it forces the hepvo to stay closed until even more pressure is built up on the shower drain side (water backing up in the tub). Once the valve opens you get a big burp of the trapped air swapping sides with the shower water. The air has to come up into the shower.
If you replace your AAV with a vent, all of those issues go away.

My kitchen sink in the '63 is like this and I just haven't taken time to add the vent. Humm. I guess I do learn from my mistakes, I just don't do anything about it!

Thanks for all the helpful info. Just to clarify, as long as I vent the shower drain line after the HepvO valve, will the shower water fill up the tank even if the shower inlet is at the low elbow of the outlet (meaning at the lower end of the tank).

[HiHoAgRV]

Yup. Done it on 2x rebuilds.

[dbj216]

Let us know how it works out. David