Note that cement (or, rather, concrete) in and of itself isn't going to hold water. It's still have to be waterproofed.
I don't know the dimensions or schematics, but my first thought would be a pond liner (basically, giant rubber sheets) and then topped with sand or other material to provide the traction.
I think a bigger issue might be to figure out how to maintain it, though. I imagine this water could get pretty nasty after a while without some form of filtration system.
The recommended, long term method
There are quite a number of places on line that sell repair parts for all types of home appliances.
It will likely be easier to purchase and install the proper replacement part than to attempt to repair a part.
Using your favorite internet search engine, look for
replacement parts <make> <model>
Where <make> = Whirlpool, or GE, or Bosch (as appropriate), and <model> = xyz, or pdq, or alpha123soup-b as listed on your machine.
and you'll probably come up with 4* options right off the bat!
*number guaranteed to be correct for as long as it took me to type it.
The short-term quick fix methods
Since the OP has indicated that he's looking for a short-term repair before replacing the appliance...
All the big-box home improvement stores stock all sorts of miracle leak stopping tapes and wraps that will work on anything from glass to plastic to metal to cement and more!!! (As seen on TV!™) You could probably even pick some up at your local 24-hour superstore while you're getting groceries.
It seems like this would be a good time to try one out and see how close it comes to the claims on its package. If one doesn't work very well, try a different brand. I've never had need to use any, so couldn't make a recommendation.
If you wanted to be really solid, but spend a bit more money (or maybe not), and can get that pipe out of there, a rubber coupling (sometimes known as Fernco connector) should be more than sturdy enough to hold in the pressure and, for only a couple of years the rubber should take the heat, as well. It might not last much beyond 2 years, but that's all your looking for.
Best Answer
The problem may not be related to a leaky seal.
Pumps of this sort would pull the liquid soap into the vertical tube and push it out the spout of the dispenser. If the pump mechanism is working correctly, it will also allow air from a designed-in vent somewhere in the cap.
For the top to be leaking in the manner you describe, it would be a failure of the pump to transport the liquid soap from the vertical tube to the spout and into your hands, not a gap or poor seal around the opening.
You can confirm this by holding the pump mechanism over an open container filled with liquid. Keep the dip tube in the liquid and activate the pump. If the liquid appears other than at the exit spout, you have confirmed a faulty pump.
The above test will also show you that a sealed container is not required for a pump to work. A sealed container will cause problems if there is not an air intake. As the soap level decreases, air must be allowed in or you have a building vacuum which will prevent soap dispensing.