When I use my basement shower, water comes up through my basement toilet flange " wax seal" yet my toilet flushes normally, what's up?

Hi WB

The basement shower is putting out more water than the 1.6 gallons per flush that your toilet does, so the PARTIAL BLOCKAGE that is in the main drain line doesn't show up until you use lots of water! Try flushing the toilet 5 times...bet it backs up pretty fast!

If these are the lowest drains in the home, my guess is that the main drain is clogged (partially) and needs to be snaked to clear the blockage, or the septic tank may be full (if you are on septic).

Dumping a full tub of water in the home will show if it is the main drain or just the branch drain that picks up the basement bathroom!

Hope that helps!

Mark