פירוש על פרה 5:3

קרויה (pumpkin-shell used as a drawing vessel, cooler) – a dry, hollow gourd/pumpkin that absorbs water.

If a pumpkin shell was immersed in water that was not fit for the mixing, it is permissible to mix in it the ashes with the water, as long as it had not been defiled. If one designs a dried out pumpkin shell to be a vessel for holding water, then he can immerse it even in a regular mikveh (water not fit for mixing) and he doesn't need to dry it off before mixing in the water to be used with the ashes. This is because the water that remains after the immersion will be absorbed into the pumpkin shell. We are not concerned lest it expel some of this water (which cannot be used with the ashes) into water that will be used for the ashes.

שהטבילוה – a mere preference for lustration, but not because of defilement, for we are speaking of something new that was never defiled.

If it has been defiled, one cannot mix in it the ashes with the water. However, if the pumpkin shell had previously been defiled then it can't be used ever to hold the water and ashes because we are concerned that it will expel some impure water that had been held in its absorbent walls, thereby invalidating the hatat waters.

במים שאין ראויין לקדש מקדשים בה – after it was wiped off. But we don’t concern ourselves that perhaps it absorbed water that are not appropriate for mixing, and it will return and emit them.

Rabbi Joshua says: if one is allowed to mix in it the ashes and water at the beginning, one should also be allowed to do so at the end; and if one is not allowed to do this at the end one should not be allowed to do it at the beginning. In either case it is not permissible to collect in it water that has already had ashes mixed in. Rabbi Joshua points out the obvious inconsistency with the previous opinion. In section one (at the beginning, before it had been defiled) we were not concerned lest it expel any water that it had absorbed. But in section two (at the end, after it had been defiled) we are concerned that it will do so. The inconsistency does not make sense. It seems that this leads Rabbi Joshua to rule strictly. Even if the pumpkin has never been defiled, he still can't use it for fear that it will expel unusable water into the living waters needed for the hatat ritual.

נטמאה אין מקדשים בה – but even though he returned and immersed it, for we are concerned that perhaps it would emit impure liquids that had been absorbed in it. For the Rabbis hold that we should be stricter with impure waters more than with waters that are not appropriate for mixing. The Rabbi Yehoshua harmonized his measures. But if you are concerned, here and there you should be concerned. But if you are not concerned, here and there you should not be concerned. But rather, whether one way or the other, whether at the beginning he immersed it in water that was not appropriate for mixing and dried it off, or whether at the end when it had become defiled and he immersed it even with appropriate [waters] for mixing and dried it off, he should not add into it mixed waters, for we are concerned that perhaps he will emit them. But the Halakha is not according to Rabbi Yehuda.

Whether or not the pumpkin has ever been defiled, it cannot be used to collect water that has already had ashes mixed in. This is because we fear that it will expel water that had not had the ashes in it, into the water that did (see the end of yesterday's mishnah). We should note that there is some disagreement among the commentators whether this last line belongs to Rabbi Joshua or to the sages.