i don't think ToS has a specific sweeper search but there's plenty of (free) services on twitter that spit em out throughout the day.
There's two ways I do it. And both require some follow up confirmation steps. Most commonly, I use an option volume screener to look for unusually high (for the time of day--north of 75% in the morning, better than 100% in the afternoon) option volume with a low put/call ratio (for bull sweepers--under .50, high ratio for put sweepers--above 2.00). The other way is if I'm going through my charts and see one. Next step is to head to your charts. You'll typically see one of two patterns. The first image shows two likely bull sweepers (but only one is), and the second is what a block order would look like (but it's not--well it is, but not of the options--and I'll tell you why) From those, you go back to the options chain, find the high volume option and pull up its chart. Find the corresponding option order and look at it's time and sales. There's a number of patterns you'll see. The top chart is UPS from tuesday, the bottom is UPS today. The first pattern (top image, left circle) will show you a series of buys, and simultaneously hitting all the exchanges on the ask. All the exchanges. On the ask. Without that, it's not a sweeper. You'll usually see a series of these orders like this while it's getting bid up (and if it's a high delta contract, the underlying will follow). So you'll have an order at (for example) .80 when the BxA was .72x.80 on all excahanges, then again on the ask at .98 when BxA was .88x.98....and so on. What that one actually was was someone buying up all the available UPS 107, 108, and 109 2/16 calls. They paid between .54 and 1.25 on the 108s and picked up about 7,000 as I recall. What they're trying to do is fire an order to all market simultaneously before someone can lift their offer seeing the activity coming their way. The second pattern in that image looks very similar, but it's not a sweeper. There was a lot of action inside the bid/ask, and there were a lot of single-exchange orders on the ask. What this actually was was people following the actual sweeper when it was reported by CNBC. (Fun fact, I was fishing for liquidity at .57 for the 108c when CNBC reported and never got filled...ended up taking it yesterday instead at .33) The last chart, today, looks like a block order. You can contrast this with a sweeper because the call volume will be a single spike rather than a mountain-like series of spikes. You identify the option from the chain as above, but when you look at the time and sales, you'll see one order (sometimes broken into two or three) for the full amount of contracts on the ask. The exchange is usually shown as FINRA (but not always). That wasn't the case in this chart though. That was a block order, but it was a covered call--the tell here is we had a low-delta option (the Friday $115), mid-spread (was .03 while BxA was .02x.05), and there's a 1:1 spike in the underlying volume. In this case, someone bought 700k shares of UPS and sold the 7k contracts simultaneously. A spec option block buyer will look similar, but the spike in the underlying will match up with the delta of the contract. If you look at these a lot, you can often know what contract it is just by the implied delta. Had the above shown 350k shares with the 7,000 contracts, you'd know that this was an ATM spec buyer being a 50-delta hedge on the underlying. TL;DR: @wallstjesus on Twitter. Ok, that's actually really funny.
I don't think thinkorswim has the option to see optionvolume from the stock itself, you have to individually check all of the options. The option screening is also not very good