Relocating a through the wall P-trap pan:
Stand the new pan on a solid floor and measure from the floor to the center of the outflow spigot. Write this measurement down and then measure from this spigot to the finished wall. Place your floor to spigot center measurement onto the wall and drop down about 3/4-inch (20 mm) below this for the true center of your 4-inch (100 mm) hole in the internal wall. Use an off cut of 4-inch (100 mm) PVC pipe and mark around it to mark off this hole. Cut out this hole and using either a wood or a masonry drill gain a hole through the outside just big enough to sight on the other side outside. Then measure down from this at center hole and remark it 1-inch (25 mm) lower to give this outside hole gradient. Note: This outside hole must be made big enough for the size of the collar on the PVC bend.
Next you must work out the gradient slope from the bottom of this hole to the bottom of another 90-degree bend or tee junction if a stack or vent coming down from above. Wherever this slope strikes will decide what you are to do to complete this new pan project sewer wise.
If on the ground floor and the size of the existing soil pipe is less than 4-inch (100 mm) follow it into the ground and below until you can reach and join in where the drain is 4-inch (100 mm).
If coming out of the wall on the first floor or higher up. If not 4-inch (100 mm) diameter to begin with. Lower the bend or the tee in this 3-inch (80 mm) PVC line and then run this section of piping in 3-inch (80mm) all the way to the pan using an 80 mm pan connector at the end.
Note: If possible always go to 4-inch (100 mm) size pipe for this run from the new pan.
Note: To either connect into a copper or lead soil pipe or cast as the case may be use rubber couplings. If having to work in a tee junction you will have to use a rubber coupling for this top most joint anyhow. Simply slide the rubber coupling up over the top most vent or top stack pipe fit the tee and then slide it back down. Sometimes it may be necessary to use a second rubber coupling below the tee to ease the union of these rigid PVC fittings into place.