From Point By Point Summary of Tosfos-
>>1. Clarification (cont.): Whereas what became Tamei via liquids (See Maharshal, Chidushim) is only Tamei mi'de'Rabbanan, and does not resemble repairing.<<
Why do we assume that it can be only Tamei mi'de'Rabbanan
Why can't we say that it could be an Av because it was in contact with a corpse or other avi avot?
Alan, Rechovot, Israel
Indeed, if it was in contact with a corpse, etc., it would become Tamei mid'Oraisa. However, the case that Tosfos is referring to is where that is not what happened, but rather what happened was that the utensil became Tamei via liquids.
(I think, Yosef David, that possibly what you may be referring to is what Rashi on Chumash (Vayikra 11:34) writes, that Vlad ha'Tum'ah cannot be Metamei a Kli. However, Tosfos in Beitzah (14b, DH Mipnei, which is in fact cited in the Maharshal which you have quoted) writes that the fluids of a Zav or Zavah can be Metamei a utensil. The Maharshal (in Chochmas Shlomo there, 14b) writes that the rule that a Vlad ha'Tum'ah cannot be Metamei a Kli means that it cannot be Metamei a Kli unless it is a liquid.)