You and/or the dawg getting in and out dripping wet will cause water to collect in the bottom. The Rubbermaid tanks all have an 1-1/2" drain with plug in the front center bottom. You could insert the plug from the inside of the tank and pull it to drain provided you are definitely above the high water mark and you placed the tank on blocks.

However, I packed the soil below ours and slightly tilted the tank to the front and one side so all water collects in that one area. Then I use a plastic bleach bottle with the bottom cut out as a bailer. A few scoops is all that's needed to empty the blind.

There are some moulded in ledges all around on both ends of the inside side of the tank that work just great for a plywood bench on each end. I cut a piece of 5/8" ply to fit and gave it two coats of paint. Made it a little undersized so it was easy to lift in and out for cleaning. I use only one on the dawg end for them to sit on and it keeps their butt up out of the water. That's important during freezing weather. Truth is, they even have a small padded cushion we made for them to sit on that fits over the plywood. You can see that it makes their seating about 1/2 the distance from the top to the bottom. That makes it easier for them to jump in and out. I use it as a step to get in and out because it's 2 feet plus from top to bottom and easy to slip when wet so that bench helps alot.

The white rod? That's a fibeglass flag holder for bikes from Walmart for $5 or so. Worked great but eventually I ended up using all PVC pipe.