I'm using this build from filtersc. It's basically a MMM build (Marine, Marauder, Medivac) with +1 attack, stim, and combat shield. I feel like I win every single game using it except those against opponents who mass tanks. How do I counter this with the build that I have?
There are two answers, assuming you can't simply outplay your opponent.
Drops means you utilize your Medivacs to attack areas where he has few tanks. Tanks gain their power because they are able to eliminate large groups of units before those units have a chance to fire. When there are only two or three tanks, they can't really do this and so you're capable of taking fights that are very cost-effective for you. As soon as the game swings beyond 3-base vs. 3-base, you have a huge mobility advantage and with 2 or 3 full Medivacs you can easily deny your opponent expansions or take out under-fortified troops. At this point, the only thing you really have to fear is a single massive attack. Beating this attack can be difficult but the main reason you'll beat it is again, with drops. As you see him start to move out, drop a few full Medivacs into his production line and that way you'll force him to pull his attack back or win the game outright with no reinforcements. Then you'll just have to trade effectively and
With Sky Terran, or air play, you gain a higher Viking count and use it in conjunction with Banshees and later possibly Battlecruisers or Ravens to force unsieges and win engagements. You can do this because you should have significantly more gas than your opponent, as he's invested into Tanks and you haven't. This also gives you free reign to drop as you please. The main issue here is that transitioning to Sky Terran leaves you very open to an attack as you do so, because he'll be hitting the critical mass of tanks that he needs to devastate you with an attack just as you start to gain air control.
The only other answer is to outmicro him by picking off out of position tanks, splitting units effectively, flanking, dropping lines of units into his tank line to negate their splash power, etc.
Countering Siege Tanks with MMM is not that easy and there is no cute timing that will help you win. You have to rely on multiple factors to secure your win.
You cannot lay back, expand get your tech and your MMM ball and a move to the win.
Here are some tactics that you can incorporate into your game:
If you drag the game into the very late game try to go air. A Battlecruiser, Banshee, Viking mix with some Marines in the back will crush Siege Tanks. He has to rely on Marines to counter this because of his huge gas investments.
You can try using banshees.
If you go MMM, then you'll have some tech labs with your Barracks. Swap them with your Starport and make some Banshees. If you want you can research stealth too. Anyway they are pretty good against tanks ;)
If you have stealth you can hide the banshees. The best way is to attack with just one stealthed banshee so your enemy will waste his radar for just one banshee. You can then attack with all your stealthed banshees. Otherwise you can focus tanks and try to attack Marines with your Marauders.