Thetford Marine Down Kit f/Small Porta Potti Models Hold 92921. Due to the special requirements of holding tanks the hold down lids have been designed to "hold down" (to slow down) the flow of urine from the bladder; however they have not been designed for this purpose. The Hold Down Kit for Small Porta Potti Models is a better solution to an easily broken part. The new design of the hold down arms have more force behind them which helps to prevent damage to the hold down handles and the porcelain of the toilet. They also aid in preventing breakage to the porcelain of the toilet. Specifications for Thetford Marine Hold Down Kit f/Small Porta Potti Models: Manufacturer: Thetford Marine Color: Black Package Contents: Thetford Marine Hold Down Kit f/Small Porta Potti Models Thetford Marine 92921: Down Kit f/Small Porta Potti Models Hold