mitsubishi ductless split a/c unit with clogged drain hose (long)

[romanowski72]

So I got a ductless split a/c unit with a, I think its 1/4" hose that is plugged up with looks like orangey pinkish mildew I would guess. whatever it is, its a slime. It reaches all the way down to the rain gutter which is a long ways, might be 50-75' of plugged line.
What is the best way to clear this out. Will a small compressor have enough power to blow the line out, or is there a chemical that wont eat the drain hose.
What causes this? This bar has to identical units and one is all plugged and the other is completely clear.

[Brian_UK]

You could try a commercial drain cleaner containing sodium hydroxide, caution it burns on skin contact so wear gloved and goggles.

[monkey spanners]

Could you blow it out with nitrogen or similar?

[MikeHolm]

You sure it is 1/4" hose? Way too small for such a run

[pcvh1976]

Renew the hose, it is a bit work but after it no more trouble. you and company earns money and costumer is satisfied.