It's easier to add an extra coupling now while he's already welding. I'd put 3 in. Drain bulkhead, thermo, site glass. Sure you can use fittings to double up the drain and site glass, but it does protrude pretty far then. Putting the site glass on your drain causes a siphon break unless you remember to plug up the top of the tube. If you want a site glass at all, a dedicated coupling is ideal. You can use a half coupling for the site/thermo but make sure you use a regular one for the drain. I'd put the drain 1" above the skirt weld, the site glass same height but rotated around a few inches, and the thermo about 4" above that.
Site glasses are nice luxuries on the HLT for measure dough-in dispensing into the MLT. On the BK, it tells you the volume of your first runnings and then later your boil (and boil off) volumes. No need on the MLT. I want to integrate them on mine because the only other way to know the volumes is to drain off into a graduated bucket.
