You can buy a manual hand pump which will suck water out of a kayak with a lot of pumping and some kayaks even have an electric pump installed. This project aims to take an inexpensive syphon electric pump and makes it waterproof so it can be used while kayaking.

Supplies

Electric syphon pump

Mountain bike inner tube

Step 1: Waterproofing

Cut a length of about 20cm from a mountain bike inner tube.
Place the inner tube in an oven set to a low setting for a couple of minutes to soften it a little (I used an airfryer set to 80c).
Stretch the rubber tubing over the battery/switch end of the syphon pump and pull down.
Secure with a couple of tie downs to make a seal with the pumps body.

Step 2: Fold Down and Roll End

Make the open end of the tube waterproof by folding a couple of times and rolling up into a mini 'bedroll'.
Secure with a couple of small tie-downs.

Step 3: How to Use

Place the pump into the water.
Turn the switch on.
Water is suck up and pumped out.

Step 4: River Test

On a recent kayak trip the pump was tried out. It pumped water and was water proof. It was found not to float so a pool noodle will be fitted over the shaft. The pump fitted nicely in the kayak between the seat and kayak's side.

Step 5: Boat Washing

Where the pump has been most useful is when washing boats down after they have been out in the water. Being able to easily suck the water out from the inside of the kayak saves having to turn the boat upside down and sea-saw it from one end to the other. This is especially useful for a double kayak.