For those who are recirculating wort during the mash, use a pump to vorlauf or are simply sparging as normal, the return line should always be kept below the wort level. The traditional lawn sprinkler type return is too susceptible to oxygen ingress. A simple hose submerged can be all that is needed. I have found a simple hose inserted through a stainless steel coupler can dip the hose output below the level of the wort.
I took a different approach, since I basically seal my mash tun and never touch it again until mashing is over. In order to prevent channeling, I wanted something to give me a more even dispersion back into the tun. I had previously used loc-line and love how it worked so I chose to continue with that.
I started with a spare lid for my kettles. The way this lid sat on the kettle, i was able to just remove the lip around the lid edge with an angle grinder and get a nice mash cap lid:
I then drilled and mounted the loc-line:
For reference, here are some additional images from Derek’s small batch setup:
So I basically lock in place so the loc-line is submerged, then I place a normal lid on top. This minimizes surface exposure as much as possible, and works great! Links to loc-line: