I've had problems downstreaming chems with my extension wand (24')too! Everything else will be working fine, dual lance, single lances with soap tip, but once in a while when I switch to the extension, I can't draw chems.
It doesn't seem logical that it's due to being fully extended, as we're already pumping through 200' of pressure hose. Another 24' doesn't make sense. Could it be that when the chem level in the bucket's low (1 gal or less in a 5 gal.) that the gravity weight (amount of chem in the bucket) makes a difference? Reason I ask is that when I think about it, this seems to be the scenario when I have trouble.
Generally, I don't have a problem soaping with my "big wand". But it always seems to happen at an inconvenient time. Any help is appreciated.