35' argosy capacitance sensors and dump valves.

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Hi all,
Fairly new to all this but had a couple of questions. I am in the process of doing a major overhaul on my 1988 35' Argosy fifth wheel trailer. In the process a lot of things are assessable that are not normally easy to get to.
1. the tank sensors are a capacitance type which simply have about 1" square copper plates which were originally just taped to the tanks with aluminum tape. The tape has loosened over the years and was thinking of something more permanent like using a epoxy to fasten the copper. Would like to install newer type indicators like the "See Master" or JRV but with all the other repairs $ is running tight.
2. I am most definitely going to replace the dump valves as they are right in the open now. Both are in line 3" valves and the grey water looks original and is a Thetford but is pretty funky looking with age. The PO replaced the other with something which looks like a wally world special and has no makings and is leaking. Anyone know what Airstream used on these Argosys?
3. All plumbing is "black pipe" Is there anything special here or can I use plain old white sewer PVC for the parts I will have to cut.
Any ideas or suggestions are welcome. As I do the project I will take pictures and post here. Thanks much