Grey Water Plumbing Question

[dbj216]

For you plumbers out there. We're re-plumbing the grey water drain system in the 76 Sovereign. The old system was quite convoluted and we think, think we can simplify it.

All the grey water drains are on the curb side along with the grey water tank. We have the galley sink, the shower pan, and the vanity sink. There are two vent stacks. One just after the galley sink, and one at the rear of the tub.

I would like to run one 1 1/2" ABS line from the galley sink drain to the tub. I would connect the vent pipes along the way giving the "drain manifold" plenty of air seems to me. All three basins have traps on their drain assemblies. I would dump all this wash water into the grey tank in two places. The grey tank would be vented through the drain manifold, not a dedicated vent line like the blank tank has.

Certainly my house has various sinks, toilets, tubs all draining to the septic tank. There isn't a separate drain pipe for each fixture.

The photo below shows a possible piping layout. Galley sink pipe is on top, and the tub drain is at the bottom if the photo. The vanity sink would drain from the photo right side. The grey tank is under the tub.

Is there a problem with this arrangement in the 76 Sovereign that any of you have experience with?

David

[Belegedhel]

The only problem I see is that your manifold venting will only work if there is a rather smooth, non-pipe-filling volume of water running down into the tank. If you should suddenly drain an entire kitchen sink full of water, you will likely get some gurgling, burbling, stop-and-go drainage ( and you may end up filling the shower pan with your kitchen dish-water). This arrangement exists in some of the more modern trailers, and there are several threads on these forums, where the owners are trying to figure out why a sink full of water doesn't drain smoothly. Otherwise, you can put as many draining things on the same manifold as you want. The best results are likely to be obtained with a dedicated vent line, though.

good luck!

[dbj216]

Thank you Belegedhel for your thoughtful reply. I thought about a rush of water from the galley sink wanting to run backwards through the shower trap. The galley sink drain line has a vent as Airstream installed it. Shower tub drain is combined with the vanity sink all on the rear of the trailer vent line. I think this is okay as the tub is almost never filled, and the vanity sink is a low flow item.

I can easily dedicate the galley sink drain line straight to the grey tank. And I can plumb the shower drain line and vanity drain line and rear vent into the second drain port in the grey tank. That way galley sink water can't get into the tub backwards through the trap.

These simple "vacuum breakers" or "air admitters" devices in a drain line can help insure water can keep flowing down the drain. I plan on using one after the vanity sink drain.

David