While RRS do not specifically prohibit it, it does put you at the mercy of RRS rule 55, the Sailing Instructions, or the protest committee. Because of this most boats no longer do them, either having their Spinnaker's modded with Velcro, or doing string drops, or simply got better at launching. For this year's Rule Book, the rule has been modified to allow the penelty to be at the discretion of the sailing instructions, something that it didn't explicitly say last year. Half the people I know use a plastic garbage can with the bottom cut out.
Rule 55 (Trash Disposal) In addition to its prohibition on competitors intentionally putting trash in the water, which supports the Basic Principle (Environmental Responsibility), rule 55 now states that this rule applies at all times while afloat (which formerly was stated in the preamble to Part 4, Other Requirements When Racing), and that the penalty for a breach of this rule may be less than disqualification. For instance, this will permit protest committees to use their discretion on whether, and how much, to penalize a boat for allowing sail stops to fall in the water after a spinnaker set.
What size boat? Surely not the C25.