There should be two drains under the filler cap - one is for water ingress around the cap, the other is for overflow of fuel. looks like the fuel treatment and the agitation caused by riding are a dynamic mix. Maybe next time, drain the tank instead of fuel treatment.
These drains are easy to clean, though you will have to remove the tank. These have been known to get blocked with normal crud (as distinct from abnormal crud). I have had to drill my nipple out where the drain hose attached. I used a very small drill < 0.5 mm in dia.