Volume Problem

A woman has a diaper pail with capacity c.  She needs to fill it with g gallons of water and gradually add d diapers to the pail.  Each diaper has a volume of v when dry and w when wet.

 

c > g + d*(v + p) where p is equal to the amount of p or poo already in the diaper before it enters the pail.  v + p < w

 

Solve for g.

 

Seriously, though.  What is the scientific way to go about this?  I always wind up with either:

 

1. so much water that even though there is more room in the pail, the water will overflow if I put in any more diapers or …
2. too little water so that even though there is more room in the pail, I can’t get all the diapers below the water line.

 

How can I figure out the right amount of water to add from the start so that t_n > t where t = amount of time between loads of diaper laundry!?!