French Drain PVC Size

There are two practical ways to deal with this. Before getting into details let me say that you should stop trying to join the trap parts of metal pipe to the trap parts of plastic pipe.

Method 1. Remove the metal pipe with the J bend and complete the P trap with plastic parts. Then join the plastic pipe to the down flow drain system where the pipes are straight and concentric with each other. There are slip type couplings to join the plastic to the metal in this way.

Method 2. Take out the plastic P trap parts and then re-build the connection from the metal J bend up to the drain of the sink using compatible metal parts. Note that metal parts are much more expensive and harder to work with so take that into consideration when selecting which method to use.

Do be aware that it may not be appropriate to be using a J bend pipe as part of the drain trap. Standing water in a trap should be confined primarily in the trap part itself and single tapered swivel joint of the trap joint. You should avoid having a situation that the standing water in the drain line rises up past other slip joints in the pipe system. Too much standing water column can also lead to a suction effect that can end up leaving the trap with not enough water in it after a heavy volume draining.

It actually isn't that bad of a place.

• Most basement bathrooms I do end up being in a corner.

• Builder planning on actual drain location is basically useless because they can't get in your head on what you will want in 5 years.

• Remember that what you are currently seeing will be covered.

• The corner location allows you to easily connect your sink drain without busting up more concrete for that. So you will bust up the concrete around this and connect your toilet and shower to a point where you have an acceptable pitch for each. Toilet will need to be relatively close and shower can be further away. Given that it is in the corner I can throw an adapter on the top of this and run the venting and the drain from sink through the walls. If this was in the middle of the room you would have an extra line that you would have to connect below grade for sure.

• Given this configuration and a "normalish" bathroom you could bust up concrete with just sledge hammer and have toilet, shower, and sink lines completed in a couple hours. After it gets inspected you could have this concreted the same day if you can line up your inspector right and if he trusts that you will have it completed (you would have cut the top off and framed beforehand if you want it done quicker).

So really if I am doing a bathroom this is a great place.

Edit: Since the OP added that they are installing a french drain on the perimeter my advice would to leave this in tact and work around it. There is no reason this should really affect a french drain system.