die Röhre
tube / pipe
A long, hollow, cylindrical object used mainly for carrying liquids or gases.
Die alte Wasserleitung besteht aus rostigen Röhren.
The old water line consists of rusty pipes.

tube
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tube / pipe
A long, hollow, cylindrical object used mainly for carrying liquids or gases.
Die alte Wasserleitung besteht aus rostigen Röhren.
The old water line consists of rusty pipes.

The word 'Röhre' (tube) is closely related to 'das Rohr' (pipe), which also describes a long, hollow object. This connection helps you understand the basic meaning of the word, which is present in almost all uses.
Durch die Röhre fließt heißes Wasser.
Hot water flows through the tube.
You can recognize the meaning of 'Röhre' (tube) from context. If it is about lines or construction, a physical tube or pipe is meant. In connection with media ('vor der Röhre sitzen' — to sit in front of the TV), it means an old television. In electronics ('Verstärker' — amplifier), it refers to a component.
Die Abflussröhre unter dem Waschbecken ist verstopft.
The drainpipe under the sink is clogged.
The idiom 'in die Röhre gucken' is fixed and means that someone gets nothing or is at a disadvantage. The person who gets nothing is the subject of the sentence.
Wir kamen zu spät zur Party und mussten beim Essen in die Röhre gucken.
We arrived at the party too late and had to lose out when it came to the food.
The term 'die Röhre' for a television is colloquial. It is often used in the expression 'vor der Röhre sitzen' or 'in die Röhre schauen' to mean 'to watch TV'.
Er verbringt jeden Abend Stunden vor der Röhre.
He spends hours in front of the TV every evening.
When referring to a physical tube or pipe, typical verbs are 'verlegen' (to lay), 'einbauen' (to install), or 'austauschen' (to replace). Liquids or gases can 'durch eine Röhre fließen' (flow through a tube).
Ein Handwerker muss die kaputte Röhre austauschen.
A tradesperson has to replace the broken pipe.
management / line
'die Leitung' and 'die Röhre' can both refer to something through which water, gas, or other substances flow. 'die Röhre' mainly describes the shape: it is long, hollow, and round. 'die Leitung' describes the function more: it transports water, gas, electricity, or data from one place to another. So a 'Leitung' can be a 'Röhre', but also a cable. Learners may confuse the words when talking about water or gas. As a practical rule: if the shape is important, 'Röhre' is more likely to fit; if the transport or connection is important, 'Leitung' is more likely to fit.

Mina findet im Keller eine alte Röhre aus Metall.
Mina finds an old metal tube in the basement.
Wegen eines Schadens an der Leitung hatte das Haus am Morgen kein Wasser.
Because of damage to the line, the house had no water in the morning.