I have an 80mm PVC drain riser at the centre a shower alcove coming up out of a concrete slab floor.
I would prefer to install a moulded PVC shower base than tile the shower alcove floor.
How do I connect the drain riser pipe to the shower base waste outlet?? Once the shower base is lowered into final position on the mortar bed I cant get underneath to connect anything up so how do I connect before lowering the base??
Depends on base you get some have rubber ring that has to be installed and forced around pipe, some you can pour hot lead in and caulk. It also depends on what kind of pipe you have. If you have castirn you pour lead. If you have PVC you can pour lead but you have to know how, but in your case use rubber ring that comes with it grease it good before you install it.