I am setting up my aquariums so that when I turn off the pumps, the water will drain into a tank to a level that will be above a 1" hole/bulkhead in the side of the tank.

I want to gravity drain the water above this hole to the wastewater drain in my house. The closest drain pipe I have is about 8 feet from the tank and is the drain for the washing machine. The pipe is 3" black pvc that the washer hose drain stuffs into the top.

Can I put a tee/wye/sanitary t on this pipe and drain the aquarium tank water into this pipe? If so what type of wye/tee should I use. What diameter pipe (8' run) and how much slope do I need. Should I use some kind of one-way valve on the aquarium tank drain pipe to make sure the washing machine doesn't backup into the aquarium?

Any ideas would be appriciated.