i'm having issues with Tapatalk as well. The submit button for new posts is showing in the same space as the Android status bar at top. I have to rotate the screen to be horizontal to be able to submit a new post.
foam cannon concentration would be higher than a foaming sprayer. you don't have to work out the PIR for a foaming sprayer, you just mix it up to that percentage since it isn't getting diluted by additional water like a pressure washer foam cannon.
If you're doing the PIR test, you can record the volumes in whatever you want. You'd just need to convert them into the same units. You could even measure the bucket by weight and convert to volume. If you want to post numbers, I can figure it out.