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With the hole made, you take whatever is necessary to scrape out the seeds and fluff. Spoons work well, just don't damage the opening so the cork will not make a tight seal. Next, get a few handfuls of gravel, the sharper the better ( don't use sand or very fine gravel which could stick inside). Pour them into the gourd and shake for a few minutes then pour out. This may have to be done a few times. This gets the fluff out.
Now we are ready to make the canteen capable of holding liquid without it tasting like swamp sludge. In this procedure I use paraffin wax and a heat source. As you all should know paraffin is extremely flammable and it can be dangerous if used carelessly so I'm not responsible if you flame your gourd, kitty (which may not be a bad thing) or your humble abode in this next step.
I use pure canning paraffin as opposed to beeswax because beeswax can make the water sort of taste well, like beeswax. Gourds I have waxed with this method have held out over the years with its original application, however the larger, more often used storage bottles I usually rewax every few years until they get too heavy from all the wax coatings.

The initial waxing is the most important since this can never be undone or redone. So take care - be careful - take your time and you will have success. I use an electric stove and oven in this process so there is no open flame. If you choose to do this on a gas stove it could be dangerous, so please take care. Get your gourd, a coffee can and a cork that fits the gourd. Also, some towels or rags to handle the hot gourd will be necessary. I set my oven on 250-275 degrees and place the dry and cleaned gourd on the middle rack. Then I take a coffee can which is clean and bend a spout in its side to use as a pouring aid. In this can I carefully melt down two hunks or slabs of wax. When melting wax watch it carefully. Melt at low heat and just as the last solid bit disappears it is ready. If you leave wax to heat too long you may lose track of how hot it is getting and it could burst into flames. As soon at the last traces of wax just disappear in the can take it off the heat. From here on in this must be done quickly and without hesitation to achieve the initial coating in the gourd. The gourd is removed from the oven and quickly you will pour the melted wax inside it (not near a source of flame). Put the cork in the hole and start vigorously shaking it for a few minutes until the liquid wax starts to "feel different" as it starts to solidify. Then quickly take out the cork and pour the excess back into the can. Set the gourd aside to cool slowly. Don't touch until fully cool. If you did this initial step correctly all of the pores inside the gourd, including whatever fluff remained, are encapsulated in wax. You can do up to two more applications of wax but do not put the gourd back in the oven because you will undo all your hard work. Just melt the wax in the can as before and pour in the gourd, shake vigorously and pour out. Let the gourd cool thoroughly each time; otherwise, you will remove the previous wax. All you need now is a new clean cork and a method of carrying it and you have a fine water container. I never used this type of container for liquor because they may adversely affect the wax.
See just that simple