We live in Virginia, and our basement used to get a significant amount of water in heavy rains. If I were you, before I spent a dime on flooring or anything else down there, I would find out definitively where the water is coming from, and how it is getting in, and then fix it. The prospect is scary, and can be expensive, but the potential for mold and mildew that you can't see, and for structural damage to your foundation from water piling up against the wall, or standing in the wall, even when it doesn't flood, is scarier. We took off some cheesy masonite paneling and discovered that the insulation and the wallboard underneath was black with mold up to our shoulders. We learned from two engineering reports that our saturated soil was actually putting so much pressure on the block foundation wall that it was beginning to bow inward. Our contractor dug down to the footings on two sides, jacked the wall back into position, added steel supports to the inside of the foundation wall, put in a new drainage system, including underground extensions of our gutters into the drainage pipes, waterproofed the walls on the outside, added a layer of this plastic stuff that carries water directly into the footing drain, and backfilled with soil that drains well. It was drastic, and expensive, and it worked like a charm, and now we are the only people in our neighborhood who have a dry, dry basement. It was worth it. I bet you can solve your problem more easily than that, but I urge you to at least find out. With all best wishes...

When you installed the trap and drain, it was cemented together, right? What are you using to seal the drain? Meaning, is it effectively sealed? The 1/8" water loss could be from a few things. When you pour water on Kerdi, the fleece can hold air bubbles on the fleece surface. As those air bubbles escape, and as the thinset absorbs some of the water, the water level will drop. A small effect. Around the drain. If you think you have a bad seal between the kerdi and the flange, run a bead of Kerdi Fix right at the seam where the Kerdi meets the flange. Clean the surface, run a bead, and smear it so it lays flat. That'll seal it. Now the corner piece that you said had a bubble behind it, and air/water leaked out? That's the only place I'd say really needs a closer look. I'm not sure how "flappy" that corner piece is, but you can either seal it in place with more Kerdi Fix, or you can slice the bubble, inject a little thinset behind it, set it flat, let the thinset cure, then cover the repaired area with another piece of Kerdi with 2" overlap extending past the sliced area and on to the "good" kerdi. Give those repairs time to cure, then try another water test. You can partially fill the pan to make sure you're not leaking at the drain of the drain flange. If successful, then you can do a full-depth water test. Let the water test run longer, too. You may get that 1/8" drop, then no more drop. That usually signifies the drop was due to entrained air coming out or water being absorbed by the exposed thinset. Mongo

1/4" drop per ft. is not enough for proper drainage. I would go with a 1/12 pitch minimum. For a deck 24' away from the house you need enough clearance to bring it down 2'. Do not use corragated metal if you mean that wavy stuff, it does not seal well at all. I use rainguard roofing that is painted all ready, not the galvalum, as it holds up better. The rainguard has a double hump at the overlap which makes for a good seal. If you have to cheat a little on the pitch then seal the overlaps with a good silicon sealer or NP1 sealer. You can always frame in the area from above the metal roofing to the rim joist on the deck & cover it with siding. This can be a problem tho cause leaves that get thru the cracks in the decking can clog up at the end of the roofing where it's closed off. Al

Having had a washer overflow this summer which required replacing sheetrock, ceiling, and carpeting, I second romy718's advice. They'll bring out a water detection device and check all the walls and floors. You'd be surprised how far water will travel. If there's any remaining at this point, it's considered gray water and they'll need to remove materials. I would also call your insurance company and find out who they recommend make the evaluation.