I tried the spaflex and found it to still be a little too rigid which caused the return pump to not sit flush with the bottom because of the memory in the tubing. I switched to silicone tubing which is very flexible, doesn't kink as easily as nylon or spaflex tubing and when rolled out stays virtually flat with no memory. The pump now sits flush after installing the silicone tubing.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1