I used the Avid Aqua magnet mount cuz I already had one and I wanted to develop a few fun projects using it. You could make your own magnet of course, but outside of that, anything else is permanent and that's exactly what I was NOT going for. Slap it in any container of any size and never have to worry about overflowing your vessel (I promise you I've done that at least 5 times if not more). The volume indicator is just a fun optional thing, use it or don't. I actually do use it as I vary the volume of water I make for my phyto all the time based on how many cultures I'm splitting so that's handy. The indicators slide up and down so calibrate it to your container. No two 5 gallon pails are born alike... A drop of CA glue will tack it in place and prevent it from moving around afterwards. I bought the float valve years ago from big reefing store (BRS). You can print multiple volume indicator rails (or portions of) and join them together with a coupler for additional length if you need it and you can break them down after each use if you so choose to do so. Source yours how you like, you may need to alter the hole size for anything different. The 'john guest' style bulkhead fitting is very std so you shouldn't have any issues there. I'll provide links below for example purposes. The RO tube is 1/4".

bulkhead fitting https://www.bulkreefsupply.com/1-4-push-connect-bulkhead-tank-adapter.html

float valve (you do want the adjustable arm) https://www.bulkreefsupply.com/adjustable-ro-float-valve.html?queryID=05ce015aefb08489d10f541eb9152dfc&objectID=851&indexName=brs_prod_m2_default_products

Avid Aqua Magnet https:\givegoogleaspin.tryharder