You can use varp 261 to fill the pouches, there is only a single varp for all three pouches, but the values of the varp contain information as to what pouch is filled or not. For every configuration of filled pouches (e.g. configuration of ONLY small is filled, or configuration of small AND large is filled but medium empty) the varp value will return a unique value.
When ONLY the small pouch is full, the varp value will return 1. When ONLY the medium pouch is full the varp value will return 2. When ONLY the large pouch is full the varp will return 4. Every combination of filled pouches is simply the sum of these values (e.g. configuration of small and large is filled, the varp value will return 1+4=5, when small, medium and large are filled varp value will return 1+2+4=7). You can use this to fill the pouches while the bank is open, saving you 20 runes and is also less botlike as humans also fill the pouches from the bank.
Code:
pouch_state = Varps.getAt(261);
if(pouch_state.getValue()==1||pouch_state.getValue()==3||pouch_state.getValue()==5||pouch_state.getValue()==7){
//Small pouch is filled. Check other pouches
} else {
//Small pouch is not filled. Fill it with essence.
}
So you know the small pouch is filled when varp returns one of the values 1, 1+2=3, 1+4=5,1+2+4=7.
You can do the same for the other pouches. I don't have giant pouch yet so wasn't able to check.
Unfortunately, you can not really use this to empty the pouches. When you are out of the bank, filling or emptying any pouch will change the value of the varp to 0. So let's say you have filled the pouches in the bank. Varp value will return 7, even when outside of the bank. Now you walk to the altar and empty the small pouch. The varp value will not return 6 (as now small is empty, but medium and large are filled 2+4) but instead return 0 and you lose information on the filling state of the other pouches.