This is a mount for a gravity fed ATO system. This mount is a perfect fit for a 20gal long sump corner. I believe the rims for 10gal, 20gal, and 29gal are all the same, so this should work with all of those tanks. It is a tight fit, so some sanding may be required if your printer is not 100% dialed in. I have had this in my tank for ~8 months and it has not failed. You must use a float valve - buy from BRS, some ¼" polyethelyene tubing, a bucket and a shelf. Screw the valve into the hole on the mount, install the ¼" tubing, connect the tubing to your bucket and place the bucket on a shelf. One of the most reliable ATOs you can have that doesn't rely on water sensors / float switches. Please do not sell my designs.