Answer #1 (Abaye): R. Yehudah himself considers Mino like Eino Mino. In our Mishnah he teaches according to his Rebbi, who says that Min b'Mino is never Batel. (Rashi - also the Beraisa is like his Rebbi, who is likewise stringent about Min b'Eino Mino of a similar appearance, to consider it to have a different appearance.)

(Beraisa - R. Yehudah citing R. Gamliel): Blood is not Mevatel blood, spit is not Mevatel spit, and urine is not Mevatel urine.

Answer #2 (Rava): Really, he holds like his Rebbi;

The (Tosfos - case of Mei Chatas in the) Mishnah discusses a bucket that is Tahor on the inside and Tamei on the outside (i.e. through Tum'ah mid'Rabanan of liquids);

Letter of the law, it should suffice if the outside and the brim are totally in contact with the water (it could be removed from the Mikvah before the inside fills up with water). Chachamim decreed that also the inside must be immersed, lest one remove it (hastily, lest the water mix with and disqualify the Mei Chatas) before the outside and brim were properly submerged;

When the majority is Mei Chatas, he is not hasty to remove it, for even if it fills up, the Mei Chatas will not become Pasul.

(Rava): Chachamim taught that sometimes Bitul depends on the majority, sometimes on whether the minority can be tasted, and sometimes on whether it affects the appearance:

Min b'Mino is Batel in a majority;

Min b'Eino Mino is Batel if the minority cannot be tasted;

Something in which the taste is irrelevant but depends on the appearance (e.g. liquids poured into a Mikvah) is Batel if it does not affect the appearance.

R. Elazar argues with Reish Lakish (78a).

(R. Elazar): Just like Mitzvos are not Mevatel each other, Isurim are not Mevatel each other.

We learn from Hillel that Mitzvos are not Mevatel each other:

(Beraisa): Hillel used to eat Korban Pesach, Matzah and bitter herbs combined together - "Al Matzos u'Morerim Yochluhu" (all are Mitzvos. None is Mevatel another even if it is the majority or its taste is overpowering.)

(Beraisa): If earthenware shards of a urinal used by a Zav or Zavah were rinsed once or twice, they are still Teme'im;

If they were rinsed three times, they are Tehorim.

This is when they were rinsed with water. If they were not rinsed (but rather, the urinal was used by Tehorim after Teme'im used it), even after 10 times, they are Teme'im. (The Tamei urine is never Batel b'Mino.)

R. Eliezer ben Yakov says, after three times, even without water, they are Tehorim.

The first Tana is like R. Yehudah, who says that Min b'Mino is never Batel.

Contradiction (Beraisa): (When spinning flax, one wets the strands in his mouth.) If a Nidah spun flax (and it is dry), one who moves it is Tahor;

If it is still moist (from her saliva), one who moves it becomes Tamei;

R. Yehudah says, even if it was dry and one wet it, one who moves it becomes Tamei due to her saliva.

Summation of contradiction: This is even if it was washed many times (the saliva is never Batel)!

Answer (Rav Papa): Saliva is unlike urine. It penetrates deeply into flax and never fully leaves it.

(Mishnah): If it became mixed with blood of Pasul Korbanos, it is poured into the Amah. (The same applies if it was mixed with Dam Tamtzis; R. Eliezer permits Zerikah.)

Question: What do they argue about?

Answer #1 (Rav Zevid): They argue about whether Chachamim decree in the Mikdash (to distance people from transgressing) if this will cause Kodshim to be wasted;

The first Tana decrees (lest someone throw blood that is mostly or entirely Pasul), and R. Eliezer does not decree.

Answer #2 (Rav Papa): (All agree that Chachamim make such decrees, e.g. regarding blood of Pesulim.) They argue about whether it is common to have more Dam Tamtzis than Dam ha'Nefesh:

The first Tana holds that this is common, therefore he decrees. R. Eliezer holds that this is uncommon, so he does not decree.

Question: According to Rav Papa, we understand why (a mixture with) Dam Tamtzis was taught in a separate clause from Dam Pesulim, for R. Eliezer argues only about the former;

However, according to Rav Zevid, R. Eliezer argues about both. The Mishnah should have taught them together!

This is left difficult.

(Mishnah): If Dam of Kosher Zevachim was mixed with blood of Ba'alei Mumim, it is poured to the Amah;

R. Eliezer says, if a cup of blood of a Ba'al Mum was mixed with cups of proper Dam Zevachim, and one of the cups was Nizrak, we throw all of them;

Chachamim say, even if all of them except for one were offered, the remaining one is poured to the Amah.

R. Eliezer says, if lower blood (i.e. that should be Nizrak below) was mixed with upper blood (i.e. of Chatas, that should be Nizrak above), we throw some above, and consider the lower blood to be like water. We then throw some below, and consider the upper blood to be like water;

Chachamim say, all of it is poured to the Amah;

If the Kohen did not ask the Halachah but did Zerikah, it is Kosher.