I got out the 150b, 200b and Emperor 280 since they're all related filters.
If you have a 150b you definitely need to get an intake pre-filter sponge, it pulls hard enough on the intake to keep betta from getting away. I had a girl who got sucked into a U around the 150b's intake and lost her swim bladder.
The 150b is, however, the best performing of the Penguin series (including the 350) in that it has more flow than the wheel needs. The 200b uses too small a pipe to get enough flow to turn the wheel when the mechanics are dirty.
So, we start with the 150b output flange and output chute:
This model has a single flat flange with no lip on it made from high temp plastic. It is very stiff and hard to get a hold on but there are a couple cool things you can do to produce an anchor the whole width of the output. You can cut a wide section of needle-point card that is about a half inch wider on each side than the output chute and then trim it down so the top corners have tabs that stick out to the sides. I used this for quite a while on the 150b and I've since lost it but you can then use nylon thread and needle to stitch a long section of sponge onto the end of the card. I see blocking the output with a rubber banded sponge to be problematic due to the width and the lack of catch-points for the rubber band. (I also don't like putting material in the tank which can grow non-native bacteria. Rubber bands are much like the polymer used to contain anaerobic bacteria in nitrate reactors.) You can also use a bit of stainless rod stuck across that area to support a cloth ribbon (nylon again) that hangs out the output. If you use a somewhat porous material you can simply route the ribbon down around the lip then again stitch something on. Touch of super glue on the knots. (that's a purigen bag inside, I still use the 150b as an "emergency" filter for mechanical and special chemical purposes such as when I'm planting or disturbing substrate in my dirt tank) The 150b is the smallest marineland filter that accepts two slot cards. AFAIK there is no special basket made for your own media selections but there's a laaarge space in there for bags/what-not. Using an intake sponge you can generally get away with using a filter bag instead of the disposable card. Just tear the fluff off the used card and waste its carbon then use a bag or sponge/etc using the defrocked card to keep it out of the bio-wheel. The 150b usually moved about 165gph for me once I started using a 200b's intake on it (anywhere from $5.00 to $15.00 replacement part).
Now on to the 200b:
Pin-card baffle and a picture of the waterfall gate.
200b suffer from low water flow rates when their inner workings are dirty but they DO move more water than the 150b and have a much wider output with a less violent tank flow. You see on right the waterfall gate that has been modified up from the original design... still not enough. You can cut a piece of sheet styrene or acrylic to stick in behind this to increase the height of the water and reduce the width of the ports thus insuring a much deeper flow of water onto the bio-wheel. The 200b has about twice the bio-capacity of the 150b due not only to the larger wheel but also the larger internal surface area. So for a 20 gallon this is the one I'd prefer with modifications. The intake is an expanded strainer which can use intake sponges (pondmaster two inch, just jam it on) and since the output flow is less a simple card baffle like this one is enough.
The card baffle uses a section of needle-point card bent and guided over two hook pins (brass coated steel, screw end with flange). To do this I had to put two small holes into the output flange. I simply aim the short bits of the two hooks away from the filter, guide the bent card on then turn them towards each other to hold it on. This mod leaves a direction to the flow and some power but not enough to bother betta unless water is falling down from it. (no amount of baffle will stop that)
The Emperor 280:
I originally used a screw-in pin baffle that left a short upside-down J with the extension of card down the front face of the filter, it became problematic and would clog with fibers and bacteria. this one is far better.
At lowes I got a pair of nylon bolts and six nylon nuts to put on them. I used a pair of scissors (on the 150b you'll need a small drill) to put holes through the drop-face on the output (which seems to have been engineered for after-market attachments) then put the bolts through from behind. You see in the middle picture that there's a large gap from tank wall. One pair of nuts to hold the bolts in place then a layer of card and another pair of nuts. Using smaller bolts/nuts and card you should be able to make an easily cleanable sterile output-baffle using layers of card to retard the flow. I found that strong flow into this layering of the cards induces aeration. Without an output modification I wouldn't use a 280 or 400 in any tank, their flow is just too violent. They're designed for use in HEAVY fishkeeping but the 280/400's intake pipe has a superior strainer basket.
Also for the 200b and 350b I have the following pictures and video:
Bubbles makes a cameo in the video...
This baffle uses the structure of the output on the 350b as support. The 350b has a taller skirt underneath the output flow and the whole thing is slightly thicker. I figured this one out for the 200b originally but the girls would knock it off from time to time. I suppose with a rubber band after this on the 200b it would stay on. The main drawback is that some things get "sucked" into the back side due to flow. You cut a long I______I in the card then slip the top over first and catch the bottom under the lip inside the skirt.
You can see in the picture it has an output hump and I use it sub-surface. The 350b is currently working in my crack-a-day tank. Even though the 350b is technically two 200b with a single pump it has no trouble operating the wheels even when dirty. By comparison the 200b seems to have a lot of issues - all stemming from the thin intake pipe.
The 350b with these mods is firm in a 10 gallon tank.
So depending on whether you have a 150b or 200b you know what will work. You CAN get some thin stainless steel wire and make a swing that fits up to each side of the output chute and will hold some card as well.