Posted 17 June 2019 - 07:17 AM
It is not uncommon for the shower drain valve to not fully seat when being shut due to some obstruction in the valve body and gate, such as hair, gunk, and virtually anything else that could find its way down the drain, but if you're confident that this isn't the condition, then I would suspect the flushing water line at the back of the toilet. Sometimes they develop cracks in the waterline fittings, resulting in leaks, and it also isn't uncommon for that fitting on the back of the toilet to have been cross-threaded, (often right from the factory during installation.) There really isn't much else in the bathroom other than the little corner sink, which is generally not a problem, and would probably be pretty obvious if it was leaking.
"If I have seen a little further, it is by standing on the shoulders of giants."
Sir Isaac Newton
Greg & Brenda
2008 17' Casita Spirit Super Dooper Deluxe
2016 Chevy Silverado, Crew Cab 5.8L V-8, 4X4
2004 Nissan Frontier, Crew Cab, V-6 2WD
Casita Club # 2754